This invention relates to a high voltage cable terminal, and more particularly to such a terminal for use in high voltage circuits carrying high current levels.
Presently there is a trend in power transmission circuits to increase the power density in power transmission corridors, which has necessitated forced cooling of enclosed power transmission cables. Without such cooling the high current density in the conductors would create localized heating, which could exceed proper operating temperatures for the cable insulation. Cable terminals in such a system are not readily cooled however, and can impose a thermal bottleneck in the power transmission system.
A typical available self-cooled high voltage cable terminal has a conductor plate on one end and a ground ring on the other. Extending between the conductor plate and the ground ring is an external ceramic shell which surrounds an annular capacitor stack having one end coupled to the conductor plate and the other end connected to the ground ring. The conductor plate is adapted to receive a connector attached to one end of the high voltage conductor, and the ground ring is adapted to pass the insulated high voltage cable therethrough. A large amount of paper insulation is applied about that portion of the insulated cable that passes through the ground ring and the annular capacitor stack. The capacitor stack serves to grade the interface between the surrounding air and the exterior surface of the ceramic insulating shell as well as the interface between the high voltage cable and the applied paper insulation.
A force cooled cable termination is disclosed in U.S. Pat. No. 3,758,699 which shows circulation of an insulating dielectric liquid to certain internal regions of the high voltage cable terminal and then through a heat exchanger. This disclosure includes an external insulating shell surrounding an internal annular capacitor stack with a channel formed therebetween for passage of the cooling dielectric liquid. A high voltage cable has a conductor terminated at one end of the terminal and passing through the annular capacitor stack. That portion of the insulated high voltage cable passing through the capacitor stack has additional paper insulation wrapped therearound, and heat generated within the cable contained within the terminal is carried away by the circulating dielectric cooling fluid.
Assembly time of high voltage, high current terminals of the type described above is done substantially in the field, due to the requirement for manual application and adjustment of heavy paper insulation rolls and taping. The application of the insulation is variable from workman to workman, and the flow path for the cooling dielectric fluid is subject to interruption and consequent terminal failure due to overheating. Additionally, since the circulating cooling dielectric fluid is exposed to the electric field within the terminal, it must be continuously filtered and maintained as uncontaminated as possible lest its dielectric properties deteriorate and precipitate an electrical failure in the terminal down the cooling channel.
Consequently, there is a need for a high voltage, high current terminal which is substantially assembled under controlled conditions in the factory, which is self-cooled, which may be easily modified to serve in force cooled applications, and which will operate reliably.